docs: def tablet(self, x, rot=0):
          """Tablet test objective function"""
          if rot and rot is not fcts.tablet:
              x = rotate(x)
          x = [x] if isscalar(x[0]) else x  # scalar into list
          f = [1e6 * x[0]**2 + sum(x[1:]**2) for x in x]
          return f if len(f) > 1 else f[0]  # 1-element-list into scalar